Electrosensitive recording sheets



June 23, 1964 B. L. CLARK 3,138,547

ELECTROSENSITIVE RECORDING SHEETS Filed Oct. 23, 1959 FAG/MILE mam/z: rm/vw/rme ELECT/V5? //Vl/N70/P 5/2765 1. CLARK United States Patent 3,138,547 ELECTROSENSITIVE RECORDING SHEETS Bryce L. Clark, St. Paul, Minn, assignor to Minnesota Mining and Manufacturing Company, St. Paul, Minn,

a corporation of Delaware Filed Oct. 23, 1959, Ser. No. 848,393

23 Claims. (Cl. 204--2) This invention relates to an electrosensitive recording sheet. In one aspect this invention relates to an electrosensitive recording paper for facsimile signals and the like.

Trends in modern technology have been placing increasing demands on fast, convenient and inexpensive techniques for printing line copy or continuous tone images and also for recording coded information. For example, recording information, such as speech and pictorial or scientific data from high speed aircraft or satellites in orbit, is assuming considerable significance. Also, high speed printing of the output of electronic computers is still seriously limited by the fact that the final recording stage is slow in comparison to the computation rate of the machine.

Various methods of recording by means of electric signals and various types of recording media have been known, but in general prior art methods and recording blanks employed therein have been subject to certain disadvantages. For example, it has been known to impregnate paper with electrically conductive solutions, or electrolytes, said solutions being adapted to be decomposed by signal impulses so that a record of the signals is made. It is also old to cause an electric arc to burn holes in a paper recording blank, the holes thus burned representing telegraphic signals for comprising the outlines of the subject matter desired to be recorded. Such recordings, however, are only suitable for relatively coarse work where no fine gradations of tonal values are necessary, such as in the reception of telegraphic signals in general and the recording of various types of curves in connection with process instrumentation. However, in the transmission of matter, particularly of pictures and the like, where continuous tones are encountered, the range of tonal values extends from what might be termed pure white to pure black, and the above methods have suffered from serious disadvantages, such as diffusion of the image area.

One of the most Widely used types of electronsensitive paper consists of a carbon impregnated conductive paper bearing, on one surface, a metallic paint layer and, on v the other surface, a powdery light gray coating. During the recording process the light gray coating is at least partially displaced or removed by the passage of current from the stylus through the paper. Such sheets are difficult to handle because of the readily smeared, readily pressure marked surface. The current flow tends not only to alter the character of the light gray coating but also to disrupt the bonding or adhesion of the light gray masking coating to the adjacent carbon impregnated paper and to provide thereby a readily removable image.

' Attempts have been made to produce dry electrosensitive sheets which do not 'rely either on electrolytes or on the physical disruption of the sheet. Certain materials have been employed which decompose under the influence of heat generated by an electric current or which alter their form in an allotropic manner. However, in certain applications, as in various instruments measuring process variables, such sheets are subject to extremes of temperature, pressure, and the like. A satisfactory heat stable electrosensitive sheet which is capable of producing a high contrast, well defined, smudge resistant, visible image which can potentially further be electronically scanned has not heretofore been known. It is therefore an object of this invention to provide such an electrosensitive paper with the above mentioned and other advantages.

It is an object of this invention to provide an electrosensitive copysheet capable of reproducing smudge resistant, highly stable images with good definition and high contrast.

It is another object of this invention to provide an electrosensitive sheet which is resistant to pressure marking, mechanically strong and which is additionally capable of recording information which can be thereafter scanned and reproduced by electronic means.

An additional object of this invention is to produce an electrosensitive facsimile sheet capable of reproducing an image with substantially no dusting, flaking or smoking.

Another object of this invention is to provide a method for making an electrosensitive paper with the above properties.

Still another object of this invention is to provide an image bearing sheet which can be further developed by electrolytic means.

FIGURE 1 is a cross-sectional view of an electrosensitive sheet according to this invention.

FIGURE 2 is a schematic diagram of a facsimile recording system embodying an electrosensitive copysheet according to this invention.

' The electrosensitive sheets of this invention comprise a continuous electrically conductive layer and a contiguous layer comprising at least one water-insoluble, heat stable, light insensitive, particulate metal compound capable of being electrically reduced in situ to the corresponding free metal, in a matrix of a binder having a lower electrical conductivity than said metal compound, said contiguous layer being essentially nondisplaceable under the conditions of electrical reduction.

The electrically conductive layer may be any conductive material, including metal foil, paper or fabric impregnated with conductive particles, such as aluminum flakes, conductive glass, conductive plastics, etc. Flexible sheets are generally used, particularly when the electrosensitive sheet is wrapped around a rotatable roll or drum during the receipt of electrical facsimile signals and reproduction of the image. Although the nondisplaceable or nondisruptable nature of the contiguous layer or electrosensitive topcoating permits the use of a carbon'irnpregnated matrix, such as carbon impregnated paper, as the electrically conductive layer, this is not preferred because of other generally less desirable properties of carbon impregnated matrices, for example, relatively low tear strength, etc.

The electrosensitive layer or topcoating contains a binder having a low electrical conductivity in which is uniformly distributed or dispersed 'at least one water-insoluble, heat stable, particulate metal compound which can be reduced to the corresponding free metal by the passage of electrical current, e.g. by means of a stylus. This current passage results in reduction of the particulate metal compound in the dry state. The free metal thereby produced in those areas contacted by a stylus provides a visible reproduction of the electrical impulses or currents, the dark colored free metal varying in intensity with the current passed. In this manner, it is possible to produce varying tonal gradations in the image areas as the stylus scans the electrosensitive layer with which it makes electrical contact. Since it has now been found that a variety of diverse metallic compounds can be electrically reduced in this manner, selection depends on such factors as the color contrast desired, cost, toxicity, desired electrical requirements for reduction, etc. The following laboratory test procedure (Example 1) may be used to determine the utility of a given metallic compound in the electrosensitive sheets of this invention and will be used to define such electrically reducible metal compounds within the scope of this invention.

EXAMPLE 1 To a wide mouth pint jar 80 grams of the particulate material to be evaluated is charged along with grams of a :70 mol ratio copolymer of butadiene and styrene and 100 grams of toluene. One-half pint of 0.5 in. diameter glass or porcelain balls are added and the mixture is milled until an 8.5 or better fineness of grind, as measured on the Hegman fineness of grind gauge, is attained (usually about 8 hours of milling). With a 0.001" aluminum foil backing sheet positioned in a fiat bed, notched bar knife coater, the knife was adjusted to provide a Wet coating thickness of 3 mils. The above milled mixture is placed on the backing sheet behind the knife, and the backing sheet is thereafter pulled through the orifice to provide a uniform 3 mil thick wet coating. The coated sheet is thereafter allowed to dry at room temperature.

The dry coated sheet is then wrapped around a 3 inch diameter aluminum roll connected as anode to a variable D.C. source and is held securely in position by means of spring clips. A 10 mil diameter tungsten stylus, actuated by means of a screw drive lightly contacts the coated surface of the sheet and is moved progressively along an axis parallel to the axis of the metal roll. The stylus is connected as cathode to the variable D.C. source. Meters are provided to measure the voltage and current in the circuit. The metal roll is rotated at a peripheral speed of 100 inches/ second and the stylus is advanced at a rate of 75 lines per inch. The voltage is slowly increased until a current flow is noted or to a maximum of 500 volts when no current flow is detected. When current flow is obtained, the voltage is held constant to observe the effect of the voltage and current on the coated sheet. The voltage is increased in increments with similar observation until an image or darkening of the surface under the stylus is observed. Those sheets on which are produced a dark image area in this manner are then analyzed to ascertain the presence of a free metal image. When no darkening is observed in this test procedure, the metal compounds are considered non-electrically reducible for purposes of this invention and can be employed as inert fillers. The following table illustrates the results obtained in this test using illustrative materials. This test can also be run with the stylus connected as anode and the aluminum roll connected as cathode. In ordinary facsimile machines, such atures below about 200 C., preferably below about 250 C. Both organic and inorganic electrically reducible metal compounds are contemplated within the scope of this in- Vention.

Visible image reproduction on the electrosensitive sheet is dependent on the contrast or color difference between the dark free metal containing image areas and the light unreduced background. Since a dark or white image is most desirable, the electrically reducible metal compound employed is preferably light in color, usually white or olf-white. Such light colored metal compounds include, for example, zinc oxide, lead monoxide, basic lead carbonate, stannic oxide, barium sulfate, etc. However, electrically reducible metal compounds which are colored,

such as vanadium pentoxide, silver oxide, cadmium sulfide, ceric oxide, zirconium oxide, antimony pentasulfide, cadmium oxide, etc., may be used in admixture with the lighter colored metal compounds or with light colored non-reducible pigments or fillers, such as titanium dioxide, magnesium oxide, etc. Of course, in certain applications, an immediately visible image is not necessary. The ratio of filler to the electrically reducible metal compound may be varied widely, depending on the desired definition, the desired color contrast and the resistivity required for efficient reduction of the electrically reducible metal compound in the electrosensitive layer.

The binder which is incorporated into the electrosensitive layer serves to firmly affix the particulate material onto the electrically conductive substrate and to maintain the continuity or integral nature of the layer. In the reproduction of images according to this invention, the current passing through the electrosensitive sheet tends to blast or disrupt the continuity of the particulate material if insuificient binder is employed. Thus, the particulate material to binder weight ratio is maintained below 10:1, preferably below 8:1 and above about 1:2. As mentioned earlier, the finely divided particulate material, i.e. the electrically reducible metal compound and filler, if used, is uniformly distributed throughout the binder matrix. Suitable insulating binders include various organic materials such as cellulose acetate, cellulose nitrate, ethyl cellulose, polystyrene, polyvinyl acetate, polyvinyl chloride, chlorinated rubbers, butadiene-styrene copolymer (e.g. 30:70 mol ratio), polyisobutylene, poly-. methacrylates, etc. Those particular electrically reducible metal compounds requiring a higher resistance of the electrosensitive layer to effect reduction to the free metal are preferably distributed in a matrix of those binders having higher resistance to electrical breakdown, since Table I .Standard Image Formation Test [4/1 Pliolite S-7 at solids coated 3 mils wet on .001 aluminum foil] Particulate Material Binder Material Image Conditions Sheet Description Analysis Name Formula Name Description Color Formed Applied Current,

Vol ma.

Zinc Oxide Z110 Pliolite S-7.... Yes 100 10 Black lines and holes.... ZnO

Titanium Dioxide 'liOr ..d0 500 0 No evidence of image.... Lead Oxide IbO. ...--d0 450 2 Black lines and holes-... PbO

Magnesium Oxide. MgO ..d0 500 U N 0 evidence of image....

decomposition of the binder is to be minimized and preferably precluded.

- The resistance characteristics of the entire electrosensitive layer may be adjusted either by controlling the resistance or proportion of the binder and of the particulate material, or by controlling the thickness of the electrosensitive layer. It is also possible to control the resistance by controlling the fineness of the particulate particles. This resistance is regulated in such fashion as to impress sufiicient electrical potential across said layer stable, i.e. which is not decomposed at sustained temperto effect eificient reduction of the metal compound in the image areas and to permit disruption of the continuity of the electrosensitive layer. Inasmuch as the electrical resistance transversely through the electrosensitive layer is to be maintained at a substantially uniform value, with the variation in reduction being controlled by the intensities of the signaling currents or potentials, the layer thickness should be maintained at a substantially constant value throughout the useful area of the sheet. Layer thicknesses above about 0.5 mil, generally above about 1 mil, are usually employed. Ordinarily, the thickness need not exceed about 3 mils. The preparation of these electrosensitive layers with any particular electrically reducible metal compound or mixtures thereof by regulating the above factors to produce the optimum result will be readily apparent to persons skilled in the art.

When .the electrosensitive sheets of this invention are used to reproduce an image transmitted by a facsimile process, as in FIGURE 2, the passage of electrical current from the scanning stylus (l), in contact with the electrosensitive surfaceof the copysheet (2), through the sheet to the metal drum (3) rotatable about axis (4), reduces the metallic compound in the image areas to a lower valence state, in which state the conductivity and other electrical properties of the image areas is sufiiciently diiferent from the equivalent properties of the background areas to afford a unique means not only for visual recording but also for the storage and reuse of reduction with essentially no 6 the recorded information. For example, the electrosensitive sheets of this invention'can be provided in tape form and can be used to record information and data from electronic computers and the like. Such recorded information can then be reused both by optical or visual sensing means and potentially by electronic sensing means relying on the diiferential pattern of electrical properties. No satisfactory information storage sheets or tapes of this character have heretofore been found that possess this combination of potentially .valuable properties.

Because of the differential conductivity pattern resulting from the production of a free metal containing image area, these electrosensitive sheets can be further processed to alter the character of the image. Electrolytic processes, in which the electrically conductive backing sheet is connected as the cathode and the electrosensitive layer is contacted by a suitable electrolyte, such as aqueous nickel chloride, an aqueous solution of a silver salt and thiourea, etc., can be used for further development of the image, if desired.

Using the preparative techniques described in Example 1, the electrosensitive sheets in Table II were prepared. Images were obtained by using these sheets on the standard Western Union Intrafax facsimile machine. The electrically conductive material of the backing was aluminum in all runs except for Example 28, in which a carbon impregnated paper (2000 ohms per square) :was employed. All percents are percent by weight. P/B represents the weight ratio of particulate material to binder.

Table II Particulate Materials Binder Materials Image Partial Coating Sheet Image Power Example B111(1 6l Wet Color Color Ratlo Mils Name Percent Name Percent Name Percent Volts Ma.

4/1 T10 -L 48 ZnO-HO4 32 Pliolite S-7 2 20 3 Whlte Blaek 105 32 4/1 z n0-H04 7 so do 2o 3 Light Dark 12 a7 a 1/1 ZnO-HC4 do 50 3 55. 165 65 5/1 ZnO(USP) do 16.5 3 Black 80 12 8/1 ZnO(USP) do 11.2 3 Gray 75 6/1 ZnOgUSP) Ma2rbor HV 14.3 3 Black 70 15 10/1 ZnO(USP) 3 Saran F120 5 v 9.1 3 Brown 105 30 5/1 ZnO(USP) DoW 700 16. 5 3 Black--- 60 10 6/1 ZuO(USP) Ethyl Cellulose 14. 3 3 do 20 Type N22. 1

10/1 ZnO (USP) Lucite 41 9.1 3 Gray 40 22 6/1 ZnO(USP) 3 Lernac 150 14.3 3 Blac 86 30 10/1 12 g P1ioliteS7 9.1 3 do 155 4 1 Cd0 so 2 0 3 do 135 110 4/1 Ag0 80 20 3 Gray 275 260 4/1 HgO- 80 p 20 3 Black .250 105 4/1 PbCOa (basic) 40 Z nO-HC4 20 g 3 do 42 4/1 B218 0 40 ZnO-HC4 20 3 Brown 50 20 black 4/1 Bi Oa 40 ZnO-HC4; 20 3 Blaek 110 4 1 CeO so ZnO-HC4 2o 3 do 165 -.4/1 -Zr0 '60 ZnO-'HC4 20 -3 Dark 285 190 1 a 5/1 ZnQ (USP) .66 Zr.0 17 3 Bl a clg 22 5/1 Zn0(USP) v 82.7 HgO 16.5 3 do 85 17 5/1 ZnO(USP) V 82.7 H o 16.5 3 do 85 135 4 1- 1 101;: 4o {gggf g ig- 20 3 White do 130 35 2/1 -Zn0(XX602) 50 Z11O-HC4 33 V 3 Light Brown 105 40 gray. black 4/1 PbO 60 ZnO-HO4 20 3 Yellow Black 175 100 ra 5/1 ZnO(USP) 82.7 HgO 16.5 3 Bgfifln do. 165 17 4/1 V 0 v 80 20 3 Brown do 100 75 4/1 Sb S 60 'ZnO-HO4 20 3 Orange Regk 135 ac 4/1" $110; 80 20 3 Pale Light 850 150 .2 V yellow brown 4 1 a o owrnmonau 20 3 Whitedo 13 4 1' ZnO (USP) g do 20 3{ g Black... 10 40 L t 42 17 2 1 ZnO(XX602) as 335 5 17 3 whiten" Grayso 30 6/1 ZnO(USP) 14.3 3 Pink Black.-- 70 17 6/1 H2M0O4. 85.7 14 3 3 Light Grays. 220 10 gra 4/1 B1203 40 ZnO-HC4 40 d0. 20 1 Offy Light 35 45 white gray.

4/1 B1 0 40 ZnO-HC4 40 d0 20 2 Pale Dark 60 45 yellow. gray.

See footnotes at end of table.

Table lI-Continued Particulate Materials Binder Materials Image I Partial Coating Sheet Image Power Example Binder Wet Color Color Ratio Mils Name Percent Name Percent Name Percent Volts Ma.

39 4/1 40 ZnO-HC4 40 Pliolite S-7 20 3 Light Light 90 50 yellow brown. 40 4/1 40 Zn-HC4 40 do 20 4 Gray Dark 145 60 yellow brown. 41 4/1 40 ZnO-HC4 40 do 20 Yellow Black.-. 165 65 gray. 42 2/1 ZnO(USP) 63.5 3.5 do 33 3 Gray do 90 25 1 ZnO-HC4 is high conductivity zinc oxide doped with free metal, supplied by New Jersey Zinc Company.

Pliolite S7 is 0 mole ratio butadiene-styrene copolymer supplied by Goodyear Tire & Rubber Co.

ZnO(USP) is lead free, acicular French process zinc oxide supplied by New Jersey Zinc Co.

*Marbon HV9200 is a high viscosity chlorinated rubber su'p lied by Marbon Corp.

5 aran F120 is polyvinyl chloride resin supplied by Dow Chemical Co.

Co Dow 70Q is polystyrene resin supplied by Dow Chemical All of the image containing clectroscnsitive sheets of Table II were resistant to smudging and pressure marking.

Various other embodiments and modifications will become apparent to those skilled in the art from the above disclosure.

I claim:

1. An electrosens'itive non-electrolytic recording sheet which comprises a continuous electrically conductive layer and a contiguous layer thereon comprising at least one water-insoluble, heat stable, light insensitive particulate metal compound capable of electrical reduction in situ to the corresponding free metal, said metal compound being uniformly dispersed in an inorganic matrix having a lower electrical conductivity than said metal compound, said contiguous layer being essentially nondisplaceable under conditions required for said electrical reduction.

2. The electrosensitive sheet of claim 1 in which the weight ratio of particulate material to binder is below about 10:1.

3. The electrosensitivc sheet of claim 1 in which the particulate metal compound is zinc oxide.

4. The elcctrosensitive sheet of claim 1 in which the particulate metal compound is nickel sesquioxide.

5. The electrosensitive sheet of claim 1 in which the particulate metal compound is cadmium oxide.

6. The electrosensitivc sheet of claim 1 in which the particulate metal compound is silver oxide.

7. The electrosensitive sheet of claim 1 in which the particulate metal compound is basic lead carbonate.

8. The electrosensitive sheet of claim 1 in which the particulate metal compound is barium sulfate.

9. The electrosensitive sheet of claim 1 in which the particulate metal compound is bismuth trioxidc.

10. The elcctrosensitive sheet of claim 1 in which the particulate metal compound is cerium oxide.

11. The electrosensitive sheet of claim 1 in which the particulate metal compound is zirconium oxide.

12. The elcctrosensitive sheet of claim 1 in which the particulate metal compound is lead oxide.

13. The electroscnsitive sheet of claim 1 in which the particulate metal compound is vanadium pentoxide.

14. The electrosensitive sheet of claim 1 in which the particulate metal compound is antimony pcntasulfide.

15. Theelectrosensitive sheet of claim 1 in which the particulate metal compound is stannic oxide.

ucite 42 is polyethylmethacrylate supplied by E. I. du Pont de Nemours and Co.

11 Dow V9 is polystyrene supplied by Dow Chemical Co. as a viscous, low viscosity liquid.

16. The electrosensitive sheet of claim 1 in which the particulate metal compound is silver behenate.

17 The electrosensitive sheet of claim 1 in which the particulate metal compound is molybdic acid.

18. The electrosensitive sheet of claim 1 in which the particulate metal compound is conductive zinc oxide.

19. An electrosensitive non-electrolytic recording sheet which comprises a non-carbonaceous electrically conductive layer and a contiguous layer thereon consisting esscntially of at least one water-insoluble, heat stable, light insensitive particulate metal compound capable of elec-' trical reduction in situ to the corresponding free metal, said metal compound being uniformly dispersed in an organic matrix having a lower electrical conductivity than said metal compound, said contiguous layer being essentially nondisplaceable under conditions required for said electrical reduction.

20. The electroscnsitive recording sheet of claim 19 wherein said non-carbonaceous electrically conductive layer is a metal.

21. The electrosensitive recording sheet of claim 19 wherein said non-carbonaceous electrically conductive layer is aluminum.

22. The electrosensitive recording sheet of claim 19 wherein said non-carbonaceous electrically conductive layer is aluminum and said metal compound is conductive zinc oxide.

23. The electrosensitive recording sheet of claim 19 wherein said non-carbonaceous electrically conductive layer is aluminum, said metal compound is conductive zinc oxide, and said contiguous layer contains titanium dioxide filler.

References Cited in the file of this patent UNITED STATES PATENTS 2,281,013 Talmcy Apr. 28,1942 2,319,765 Talmey May 18, 1943 2,554,017 Dalton May 22, 1951 FOREIGN PATENTS 149,268 Switzerland Nov. 16, 1931 464,112 Great Britain Apr. 12, 1937 113,072 Australia May 9, 1941 962,661 Germany Apr. 25, 1957 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 l38 547 June 23 1964 Bryce Lo Clark It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patentshould read as corrected below.

Columns 3 and 4 Table 1,, under the heading "Analysis" the formula "ZnO" and "PbO" read Zn and Pb column 7 line 35 for "inorganic" read organic e Signed and sealed this 24th day of November 1964.,

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Altesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 138547 June 23 1964 Bryce L, Clark It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Columns 3 and 4 Table I, under the heading "Analysis" the formula "ZnO" and "PbO" read Zn and Pb column 7 line 35 for "inorganic" read organic Signed and sealed this 24th day of November 1964o (SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER 1 Attesting Officer Commissioner of Patents 

1. A METHOD OF TREATING TIN PLATE SO AS TO PROVIDE IMPROVED LACQUER ADHERENT SURFACE CHARACTERISTICS WHICH COMPRISES IN COMBINATION THE STEPS OF MAKING THE TIN PLATE THE CATHODE WHILE IMMERSED IN A HOT AQUEOUS ALKALINE CLEANING ELECTROLYTE AND PASSING AN ELECTRIC CURRENT THROUGH SAID ELECTROLYTE AND TIN PLATE TO REMOVE SUBSTANTIALLY ALL SURFACE OXIDES AND OTHER CONTAMINATION THEREON WITHOUT REMOVING TIN, WASHING SAID TIN PLATE WITH WATER AFTER IT IS WITHDRAWN FROM SAID ALKALINE CLEANING ELECTROLYTETO RINSE AWAY MOST OF SAID ALKALINE CLEANING ELECTROLYTE REMAINING ON THE SURFACE THEREOF, THEREAFTER APPLYING TO SAID TIN PLATE AFTER WASHING WITH WATER AND BEFORE SUBJECTING TO ELECTROLYTIC TREATMENT WITH A CHROMINUM CONTAINING SOLUTION AN ACID CONDITIONING SOLUTION COMPRISING ING A HOT DILUTE AQUEOUS ACID SOLUTION HAVING A PH BETWEEN ABOUT PH 4 AND 6, AND DIRECTLY PASSIVATING THE ACID CONDITIONED TIN PLATE SURFACE BY MAKING SAID TIN PLATE THE CATHODE WHILE IMMERSING IN A HOT AQUEOUS HEXAVALENT CHROMIUM CONTAINING ELECTROLYTE HAVING A PH BETWEEN ABOUT PH4 AND 6 WHILE PASSING AN ELECTRIC CURRENT THROUGH SAID CHROMIUM CONTAINING ELECTROLYTE AND TIN PLATE TO PROVIDE A PASSIVE NONOXIDIZING SURFACE ON SAID TIN PLATE; WHEREBY A TIN PLATE HAVING SUBSTANTIALLY IMPROVED LACQUER ADHERENT SURFACE CHARACTERISTICS IS PROVIDED.
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